1. Field of the Invention
The present invention relates to a valve apparatus.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication No. 2001-182638 discloses a valve apparatus, which can open and close a flow passage according to a displacement position of a slidable member or which can adjust a flow quantity of fluid that passes the flow passage. One previously proposed valve apparatus of this kind will be described with reference to FIG. 6.
The valve apparatus shown in FIG. 6 is implemented as a pressure reducing valve 111, which is installed to a common rail 101 of a common rail fuel injection system of an internal combustion engine (e.g., a diesel engine). The pressure reducing valve 111 reduces an actual pressure of the common rail 101 when the actual pressure of the common rail 101 exceeds a predetermined pressure.
In the pressure reducing valve 111, a pushrod (a slidable member) 122 is axially slidably supported in a slide hole 128 formed in a valve body 121. A drive arrangement 125, which drives the pushrod 122, includes a spring 141 and an electromagnetic actuator 142. The electromagnetic actuator 142 includes an armature (a slider) 143, a solenoid 146 and a connector 147 with terminals 147a. The armature 143 is fixed to an upper end of the pushrod 122 in FIG. 6 to move integrally with the pushrod 122. The spring 141 urges the armature 143 and the pushrod 122 in the downward direction (a valve closing direction) in FIG. 6. The solenoid 146 magnetically attracts the armature 143 upon receiving electric power through the connector 147, so that the pushrod 122 fixed to the armature 143 is urged in the downward direction in FIG. 6 to seat a ball 123 against a valve seat 138 formed in a seat member 124 and thereby to close a flow passage hole 137 formed in the center of the valve seat 138.
When the ball 123 is lifted away from the valve seat 138 by the fuel pressure in an accumulation chamber 101d of the common rail 101, the flow passage hole 137 is opened. Thus, the high pressure fuel of the accumulation chamber 101d of the common rail 101 is conducted through the flow passage hole 137, a small diameter hole 132, radial holes 133 and a low pressure passage 101c to a lower pressure side (e.g., a fuel tank) of the system.
The previously proposed pressure reducing valve 111 may have the following disadvantage. Specifically, the pressure reducing valve 111 is installed to and is fixed to the common rail 101 when a male threaded portion 134 formed in the outer peripheral surface of the valve body 121 is threadably tightened and is thereby threadably secured to a female threaded portion 101a of the common rail 101. Thus, there is a possibility that the valve body 121 is deformed by the tightening load (the axially compressed load) applied to the valve body 121 by a tool (e.g., a wrench) that is used to install the pressure reducing valve 111 to the common rail 101.
Furthermore, when the common rail 101 is formed by metal casting or is processed in a high temperature environment, the common rail 101 may possibly be deformed in some cases. Thus, when the valve body 121 is strongly and securely tightened against such a deformed common rail 101, the valve body 121 may possibly be deformed due to the deformation of the common rail 101.
When the valve body 121 is deformed in this way, the slide hole 128, which is directly formed in the valve body 121, may be deformed. When this happens, the pushrod 122 may be interfered with the slide hole 128, so that a trouble in the slide movement of the pushrod 122 may possible occur.
Furthermore, when the deformation of the slide hole 128 occurs, the central axis of the pushrod 122 may possibly deviate from the central axis of the valve seat 138 in some cases. When the central axis of the pushrod 122 is deviated from the central axis of the valve seat 138, the seating direction of the ball 123 against the valve seat 138 (the urging direction of the urging force applied to the ball 123) may possibly be deviated from its proper direction. Thus, the leakage through the valve seat 138 may possibly occur even when the ball 123 is seated against the valve seat 138. Also, localized partial wearing may occur at the connection between the ball 123 and the valve seat 138.
Here, it is conceivable to increase a wall thickness of the valve body 121 to limit the deformation of the valve body 121. However, this will disadvantageously result in an increase in both a size and a weight of the pressure reducing valve 111.
The previously proposed pressure reducing valve 111 may also have the following disadvantage. Specifically, when the armature 143 of the electromagnetic actuator 142 is driven in the axial direction, a volume of an armature receiving chamber 148, which is formed in the valve body 121 and slidably receives the armature 143, is changed. In order to promote this volume change of the armature receiving chamber 148 to facilitate the movement of the armature 143 and the pushrod 122, the armature receiving chamber 148 is communicated with an external space, which is external to the armature receiving chamber 148, through a breathing passage.
In the previously proposed pressure reducing valve 111, the armature receiving chamber 148 is communicated with an interior of the small diameter hole 132 (a low pressure side), which is positioned on the upstream side of the valve seat 138, through a slide clearance B between the pushrod 122 and an inner peripheral surface of the slide hole 128. The slide clearance B is relatively narrow in the radial direction and is axially lengthened to limit possible deviation of the central axis of the pushrod 122. Thus, a flow resistance of the fluid (the fuel), which passes the slide clearance B, is relatively large. Therefore, the breathing (the volume change) of the armature receiving chamber 148 may be disadvantageously hindered, and thereby movability (response) of the armature 143 and the pushrod 122 may be disadvantageously limited.